The present invention relates to a drive spindle.
In the field of machine tools, it is known to use a drive spindle which includes a tubular casing; an electric motor with an output shaft coaxial with the tubular casing and defining a tool-bearing spindle; and means for cooling the electric motor which include an impeller coaxial with the casing. The said cooling means and the motor are housed inside the tubular casing and the impeller is operable to impart to the air inside the tubular casing a substantially helical motion along the said tubular casing.
The prior art cooling device of the type described is not very effective since, owing to its helical motion, the airflow generated by the associated impeller has a relatively small axial component and thus remains for a relatively long time inside the said tubular casing and in contact with the electric motor to be cooled.
The object of the present invention is to provide a drive spindle which is free of the disadvantages described above.
This object is achieved according to the present invention by providing a drive spindle which includes a tubular casing; an electric motor with an output shaft coaxial with the said tubular casing and defining a tool-bearing spindle; and means for cooling the said motor which include an impeller coaxial with the said tubular casing; the said cooling means and the said motor being housed inside the said tubular casing and the said impeller being operable to impart to the air within the tubular casing a first substantially helical motion along the said tubular casing; characterised in that the said cooling means also include a static deflector able gradually to turn the said helical motion into a substantially axial motion along the said tubular casing.
By transforming the helical motion of the air into a substantially axial motion along the tubular casing, the drive spindle of the invention enables a greater air pressure to be generated upstream of the electric motor to be cooled and a greater volume of air to be in contact with the electric motor.